Ammonium (phenolate method) in seawater

Ammonium (Phenolate method) in seawater

(Lachat QuickChem Method #10-107-06-1-C; http://www.lachatinstruments.com/)

Principle

This method is based on the Berthelot reaction. Ammonia reacts with alkaline phenol, then with sodium hypochlorite to form indophenol blue. Sodium nitroprusside is added to enhance sensitivity. The absorbance of the reaction product is measured at 630 nm and is directly proportional to the original ammonia concentration. Note: EDTA is added to the sample in-line in order to prevent precipitation of calcium and magnesium ions. This method is often adapted for use on an autoanalyzer, to allow for automated analysis of multiple samples and replicates.